In a vehicular disc brake, a brake pad pressing spring (hereinafter, referred to as a pad pressing spring for short) is provided to prevent a brake pad (hereinafter, referred to as a pad for short) from rattling during traveling and the pad is pressed to a torque receiving surface in advance. An example of a pad pressing spring used for the object described above is also used as an indicator for detecting an abrasion limit of the pad.
The pad pressing spring also used as an indicator reduces a striking noise (a so-called clink noise or click noise) which is caused by collision of the pad against the torque receiving surface formed on a caliper or a caliper supporting member (a mount), in such a manner that the pad pressing spring reduces, using a spring force, a movement speed of a brake pad during a braking operation of rearward traveling of a vehicle. The pad pressing spring is mounted on a part of a pad back plate (a back plate of the pad), which is a torque transmitting portion on a disc-rotor (hereinafter, also referred to simply as a disc for short) leading side in a forward-traveling mode of a vehicle. An elastic arm of the pressing spring abuts on a part of the caliper or the caliper supporting member (a mounting), which is the torque receiving surface on a disc trailing side in the forward-traveling mode of a vehicle, and the spring force generated by the elastic arm presses the pad in a disc-rotor rotating direction (a normal-rotating direction) in the forward-traveling mode of a vehicle. Accordingly, the pressing spring presses the pad to a torque receiving surface on the disc trailing side in the forward-traveling mode of a vehicle.
Two types, that is, a caulking fixing type (JP-A-10-331883) and a pinching fixing type (a so-called clip type JP-A-2003-28217), of a pad pressing spring have been used, relative to a mounting type of the pad pressing spring on the pad back plate. In the pinching fixing type pad pressing spring disclosed in JP-A-2003-28217, a pair of facing pinching pieces, which pinch the pad back plate in a thickness direction, are formed in such a manner that one end side of a strip-shaped spring material is bent in a U shape. In addition, an elastic arm which generates a spring force and presses the pad in the disc normal-rotating direction is formed on a tip end of the pinching piece which is disposed on a rear surface side of the pad back plate.
A caulking fixing type pad pressing spring has a number of factors of a variation in sizes and it is difficult to precisely perform a caulking fixing work on a target position. Furthermore, there is a concern that costs may increase due to the added caulking process. Meanwhile, in a case of a pinching fixing type pad pressing spring, a caulking process is not necessary. However, when a tangential force (a load acting in a tangential direction of the disc) caused by a braking operation of rearward traveling is applied to the pad, a spring deformation mode is not stabilized. Accordingly, spring performance may be unstable due to a variation in the deformation mode, and thus there is a concern that the desired effect may not be obtained.
Two factors can be conceived as the reasons why the deformation mode of a pinching fixing type pad pressing spring of the related art is not stabilized. A first factor is that a pinched state by the pinching portions is unstable, and thus it is easy for the pad pressing spring to move with respect to the pad back plate. When the elastic arm is elastically deformed, a tip end side of the pinching piece moves outward, and thus, in some cases, the pinching piece on a side in which the elastic arm extends floats up from a rear surface of the pad back plate. In this state, the pinching piece is also elastically deformed, and thus an unstable spring force due to deformation of the pinching piece is added to the spring force by the elastic arm. As a result, a variation in the spring performance increases. A second factor of the reason why the deformation mode is not stabilized is that a variation in deformation of the elastic arm, which is caused by the displacement of the pad, is likely to occur. In the case of a pinching fixing type pad pressing spring, when the pad is pressed to the disc or the pad is separated from the disc, if a follow-up operation of a contact point of the elastic arm, relative to the torque receiving portion, is smoothly performed, a variation in deformation state does not occur. However, in the case of a pinching fixing type pad pressing spring of the related art, the rigidity of the elastic arm relative to a load in a disc axial direction is not sufficient, and thus the follow-up movement of the contact point does not be performed during displacement of the pad. Accordingly, the deformation amount of the elastic arm increases or decreases, and thus relative displacement between the pad and the torque receiving surface is absorbed. As a result, an increase/decrease in the deformation amount also causes a variation in the spring performance.